The present invention relates to an automatic switch circuit which continuously monitors the numerals being displayed by a digital meter so that the device is turned "OFF" after a predetermined interval of detecting that the numerals are not displaying a reading.
Prior art digital instruments seldom contain a built-in automatic power off function. Thus, when the user forgets to turn off the power after use, the current of the battery will be consumed continuously so as to shorten the battery life. As a remedy to the foregoing problem, the present inventor has developed a power supply system which can be switched off automatically within a specific period of time. However, it is not ideal for the power supply system to be switched off after a specific period of time, since switching the instrument off would cause inconvenience to the user if the instrument has to be continuously used.